This disclosure generally relates a preferential grain casting process. More particularly, this disclosure describes a method and device for preferential grain casting utilizing a seed to control orientation of a columnar grain casting.
Processes for orientating a grain structure in a cast article are known to provide either a columnar structure or a single crystal structure. In such processes, a ceramic casting mold that is heated to a temperature above the melting point of the alloy is filled with molten material within a furnace. This mold is subsequently withdrawn from a hot chamber to a cold chamber of the casting furnace in a controlled manner to control solidification and obtain directional alignment of the crystals. A starter block provides a starting point for the solidification of a molten material. For a columnar grain structure, the starter block facilitates the nucleation and growth of several columns that will grow in the direction opposite of heat extraction as opposed to the formation of a random grain structure without directionality. Although a columnar grain structure is an improvement over random grain structures, the column grain structure is only orientated in one direction identified as the primary orientation. Adjacent columns would possess the same primary orientation but possess different secondary orientations denoting a crystal structure that is rotated about the primary growth axis.
Accordingly, it is desirable to design and develop a method and device for providing a preferential columnar grain structure for a cast article. A process that promotes the nucleation and growth of many directional columns is preferred to optimize mechanical properties within a cast component. Because of component and mold geometries or furnace design limitations, obtaining many directional columns that progress from the bottom to the top of the casting is not always easily achievable. In many instances, only a few columns will nucleate and grow compromising part integrity.
It is desirable to develop a method that promotes the nucleation and growth of as many directional columns as possible to optimize part integrity.